Ever feel like your cat knows a little more than she’s letting on? Well, you might be on to something. New research shows that our little feline friends can be surprising sources of evidence when crimes are committed.
In particular, a cat’s fur can hold enough DNA shed by a nearby human to serve as evidence of a brief encounter between the two. This may mean that even if cats are not questioned, they can still help identify criminals.
The new study is the first to examine how pets may contribute to DNA transfer, so there is much work to be done. But this is a positive step towards more comprehensive forensic evidence collection in the future – which would certainly be really useful in police investigations.
“The collection of human DNA should be very important in crime scene investigations, but companion animals such as cats and dogs are not known to be implicated in the transmission of human DNA.” says forensic expert Heidi Monkman Professor at Flinders University, Australia.
“These companion animals can be very relevant to assess the presence and activity of household residents or any close visitors to the scene.”
In recent years, DNA analysis technology has improved so much that even the smallest traces of genetic material can be relevant to crime scene investigations. And we messy humans leave our DNA all over the place. Even a brief contact with an object can transfer traces of our genetic material. Literally Touch the DNA is not sufficient on its own to identify a suspect but may be used to support other lines of evidence or exclude people.
Touch DNA obtained from a surface does not necessarily even require a person to touch that surface. It can be carried by a number of means, such as in skin cells or hairs that are carried by the passing body. This is where pets can play a role.
So Monkman and his Flinders University colleague Maria Goray, an experienced crime scene investigator, teamed up with forensic expert Roland van Oorschot of Australia’s Victoria Police Forensic Services Department to see if they could extract traces of readable human DNA from domestic cats.
Their study was conducted on 20 cats from 15 families. At the study participants’ homes, the researchers swabbed the fur on the right side of each cat twice and collected DNA samples from most of the study participants (one was a young child who was not sampled). Later, cat swabs and human DNA samples were processed.
In addition, the residents of the house filled out questionnaires about the daily behavior and habits of the cats. This includes how often the cat is touched in the home and by whom.
Detectable levels of DNA were found in 80 percent of cat swab samples. For all cats, there was no significant difference between the amount of DNA available and the time of last human contact or the length of the cat’s fur.
The team was able to create DNA profiles from 70 percent of the cats in the study can be interpreted well enough to be associated with a person. Most of the DNA was from people in the cat’s home, but only unknown human DNA was detected in six cats.
Two of these cats spent a lot of time on the bed of the child whose DNA was not sampled, which could explain some of the “mystery” results. The origin of the unknown DNA in the remaining four cats is unknown. None of the households had visitors for at least two days before the tampons.
One case was particularly interesting: two cats, two people in a house. One of the cats, a hairless sphynx, carried the DNA of an unknown third person. The other cat, a short-haired ragdoll, did not. Both cats were mutual equal with people in their homes.
Possible sources may include direct transfer of DNA from humans, such as rubbing or scratching by a cat on a contaminated surface. DNA could also have been left over from the cat’s last contact with a visitor.
“The way this DNA was transmitted to the cat and its persistence on them is unknown” researchers write.
“Further research is needed on the transmission of human DNA to and from cats, the persistence of human DNA in cats, and what may affect the different levels of DNA in cats, such as the behavioral habits and shedder status of their owners.”
Or maybe that’s what the cat wants you to think…
The study was published Forensic Science International: Genetics Supplement Series.
